1. Technical Field
The present invention relates to a semiconductor wafer polishing apparatus polishing a circumferential edge side of a wafer, and a method of polishing a semiconductor wafer.
2. Related Art
With developing larger scale of integration of circuits, decreasing pattern size and enlarging wafer diameter in semiconductor manufacturing process, a higher chip yield has been desired. One known technique of improving the chip yield ever adopted is to remove an unnecessary portion of films formed on the bevel portion and notch portion of the circumferential edge of a wafer. The bevel portion of a wafer is slightly rounded when one views from the side, and the notch portion of a wafer is near V-shape when one views from the top surface. For this reason, the films easily peels off from the bevel portion and the notch portion of a wafer in diffusion process and those films may adhere onto the top and back surfaces of the wafer, to result in the yield loss and/or the apparatus down. Bevel polishing can prevent these problems.
As this kind of polishing apparatus, there has been known an apparatus configured as holding a wafer in a rotatable manner, and as allowing one surface of a polishing pad to freely contact with the bevel portion of the wafer (see Japanese Laid-Open Patent Publication No. 2005-26274, for example). FIG. 11 is a schematic drawing showing the conventional semiconductor wafer polishing apparatus. This polishing apparatus is configured so as to rotate the wafer while supplying an abrasive onto the surface, and to allow the polishing pad to contact with the bevel portion to thereby polish the bevel portion over the entire range of its circumference. The polishing apparatus also has a nozzle blowing a non-reactive gas against the surface of the wafer, aiming at spreading the gas emitted from the nozzle over the surface of the wafer making use of rotation of the wafer, to thereby prevent the abrasive from infiltrating into the central region as viewed in the radial direction.
However, in the polishing apparatus described in Japanese Laid-Open Patent Publication No. 2005-26274, configured as diffusing the gas over the surface of the wafer making use of rotation of the wafer, route and rate of flow of the gas vary due to changes in conditions such as rotation speed of the wafer, blowing speed of the gas and so forth. As a consequence, the gas cannot uniformly be diffused, thereby making it difficult to suppress infiltration of the abrasive by stably spreading the gas over the surface of the wafer. Blowing from the nozzle only at one point is also highly causative of charge generation on the surface of the wafer, which may degrade the device quality being fabricated on the semiconductor wafer.